GB2315537A

GB2315537A - Equipment used for the air conditioning of habitable enclosures

Info

Publication number: GB2315537A
Application number: GB9615299A
Authority: GB
Inventors: Peter William Fitt
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-07-20
Filing date: 1996-07-20
Publication date: 1998-02-04
Also published as: GB9615299D0

Abstract

An intercooler, 3, is for use in an air conditioning system which uses air as the primary refrigerant. Hot high pressure air produced by a compressor, 2, is cooled by a flow of cold low pressure refrigerant air which leaves a load heat exchanger, 8. Any water which condenses in the high pressure circuit is collected at the high pressure outlet to pass through a duct, 14, and enter the low pressure inlet, 13. Air from the atmosphere, 1, is entrained by the flow of low pressure refrigerant air and enters the intercooler, 3, through an inlet duct, 15, to supplement the cooling effect provided by the low pressure refrigerant air. The heat exchanger 8 may be used in cooling the passenger compartment 9 of a car.

Description

IMPROVEXEKTS IN OR RELATING TO EQUIPMENT USED FOR THE AIR CONDITIONING OF HABITABLE ERCLOSURES The present invention relates to improvements in equipment used in systems for the air conditioning of habitable enclosures in which air is the primary refrigerant.

Refrigeration systems using air as the working fluid conventionally incorporate expansion means, compression means, and one or more heat exchangers. In these systems, refrigeration is achieved by extracting energy from the air, in the form of work, as the air passes through an expander from one pressure to a lower pressure. Typically, air taken from the atmosphere is raised in pressure by a compressor, or compressors, and passed through a heat exchanger, or intercooler, by means of which heat can be rejected to the atmosphere, before the air enters the expander. The cold air leaving the expander is available for refrigeration.

In one type of system, a second, 'load', heat exchanger enables heat from a habitable enclosure to be transferred to the cold refrigerating air leaving the expander. The refrigerating air leaving this second heat exchanger is still at low temperature and, if passed in counter flow through the intercooler, operates recuperatively to receive heat from the air leaving the compressor, before being discharged to the atmosphere.

When using an intercooler incorporating recuperation, a 'regenerative intercooler', condensation of atmospheric moisture will be experienced in the regenerative section of the high pressure side of the heat exchanger.

This establishes a 'pinch-point' condition and causes the exit temperature, down to which the air is cooled, to be significantly higher than that of the cool air leaving the load heat exchanger. In addition, a regenerative intercooler of this type, which does not use ambient air for intercooling, avoids the necessity for incorporating a fan to pass ambient air through the intercooler, but may be too large for some applications, especially motor vehicles for which the use of air for refrigeration is particularly suitable.. This is because, by depending on the refrigerating air only to provide intercooling, there will be a low mean temperature difference between the high and low pressure streams within the regenerative intercooler.

According to the present invention there is provided a water separator in the high pressure outlet of a regenerative intercooler to collect condensate deposited in the high pressure passageways and a duct means to transfer this condensate to the inlet of the low pressure passageways, and entries for ambient air to be entrained by the flow of low pressure air through injection or ejection devices so as to supplement the cooling action of the low pressure air in that part of the regenerative intercooler operating above ambient temperature.

The first improvement is incorporated to overcome the effects of the pinch point, created by the condensation of moisture in the high pressure stream. This improvement enables the condensate to be collected at the outlet of the heat exchanger and to be transferred to the low pressure side where it evaporates as the air receives heat from the high pressure side. This evaporation improves the heat absorbing properties of the low pressure air to match the heat rejection characteristics of the high pressure air.

Although the recuperative use of the refrigerant air in the intercooler enables the entry temperature to the expander to be reduced below ambient temperature, and thus reduce the temperature of the air leaving the expander, there will be a point within the regenerative intercooler where the temperature of the high pressure air and the refrigerant air are both near to ambient temperature. The second improvement enables ambient air to be entrained by, and mixed with, the flow of refrigerant air from the point where the temperatures exceed ambient temperature. Because this additional flow of ambient air increases the temperature difference between the air to be cooled and the cooling air, the size of the intercooler portion of the heat exchanger, where temperatures exceed ambient temperature, can be reduced significantly Specific embodiments of the invention will now be described, by way of example only, in which the habitable enclosure is the passengers' compartment of a motor car. In this description, reference will be made to the accompanying drawings in which: Figure 1 shows the circuit diagram for a refrigeration system using air as the primary refrigerant which incorporates a combined compressor, expander and motor assembly, a regenerative intercooler incorporating a condensate return and provision for the supplementary intercooling by ambient air, and a load heat exchanger by means of which a secondary refrigerant circuit can transfer heat from the passenger compartment to the refrigerant air.

Figure 2 shows the typical external form of a regenerative intercooler incorporating an entry for ambient air.

Figure 3 shows an intermediate section of the sandwich construction of a regenerative intercooler incorporating injectors driven by the flow of refrigerant air by means of which ambient air is entrained to mix with the refrigerant air.

Figure 4 shows a section of an alternative construction in which ambient air is entrained by the action of ejectors driven by the refrigerant air to flow parallel with the refrigerant air before mixing near the discharge port of the regenerative intercooler.

In the first embodiment, illustrated by Figure 1, air from the atmosphere, 1, enters the compressor, 2, and upon leaving passes through a regenerative intercooler, 3, where its temperature is reduced and condensed moisture is collected at its outlet, 4. This saturated air then enters the expander, 5, where the pressure and temperature both fall. During this expansion process work is transferred by means of a shaft, 6, to the compressor, 2, to supplement the main power supplied by electric motor, 7, which receives electricity from a generator driven by the motor car engine. The cold air leaving the expander, 5, enters a load heat exchanger, 8, to receive heat, conveyed by means of a secondary fluid, from the passenger compartment, 9, of the car. This secondary fluid is conveniently an anti-freeze liquid which is circulated by means of a pump, 10, through a second heat exchanger, 11, within the car and through which air within the car is circulated by a fan, 12.

After leaving the heat exchanger, 8, the refrigerating air passes to the inlet, 13, of the regenerative intercooler, 3, where condensate from the high pressure side is added by means of a duct, 14, before the air passes through the regenerative intercooler. Within the low pressure side of the regenerative intercooler the received condensate evaporates as the air absorbs heat from the high pressure side before being discharged to the atmosphere, 1.

The regenerative intercooler incorporates inlet duct means, 15, so that ambient air can enter the low pressure side to mix with the refrigerating air and supplement cooling within the intercooler. Figure 2 illustrates a suitable external configuration of the regenerative intercooler into which hot high pressure air from the compressor, 2, enters the heat exchanger at inlet port, 16, and passes in counter flow to the refrigerating air before emerging at the outlet port, 4. After leaving the load heat exchanger, 8, the refrigerating air enters the low pressure passageways at inlet port, 13, and emerges at the outlet port, 17, to the atmosphere, 1.

Figure 3 illustrates a cross section and external view of a few layers of the sandwich construction of a regenerative intercooler incorporating the preferred means of inducing the ambient air into the low pressure passageways of the regenerative intercooler. Beyond the recuperative section, 18, of the regenerative intercooler the low pressure passageways, 19, carrying the refrigerating air are reduced in area so that the refrigerating air is accelerated. Typically, this may be achieved by introducing a false wall, 20, on one side of the low pressure passageway. The space immediately surrounding the exit, 21, of this narrowed section communicates with the inlet duct, 15, and provides a volume within which the ambient air can mix with the refrigerating air, the mixture passing through the intercooler section, 22, before leaving at the outlet port, 17.

Figure 4 illustrates a cross section of a few layers of the sandwich construction of a regenerative intercooler incorporating an alternative embodiment of the invention in which the ambient air is drawn through the low pressure passageways of the regenerative intercooler by the action of the refrigerating air. In this embodiment, a dividing wall, 23, is configured to reduce the area of the low pressure passageway, 24, which carries the refrigerating air within the intercooler portion, 22, of the heat exchanger. Ambient air is admitted immediately after the recuperative section, 18, through inlet duct, 15, to the side of the dividing wall remote from the refrigerating air, 27. This ambient air flows in parallel with, but separated from, the refrigerating air to the point where the dividing wall terminates, 25. Downstream of this point is a region, 26, where the high velocity refrigerating air interacts with the ambient air to operate as an ejector which induces the previously mentioned flow of ambient air.

It is to be understood that in the shaded regions of the high and low pressure passageways, referred to in the above descriptions of Figures 3 and 4, secondary surfaces, such as fins which run parallel to the direction of flow of the air, may be incorporated to enhance the heat transfer characteristics between the two air streams. The regions where the refrigerant and ambient air streams interact, 21 and 26, will not normally incorporate secondary surfaces and are configured to maximise the entrainment action of the low pressure stream, and minimise the flow resistance to the mixed stream.

Claims

1. A heat exchanger used as a regenerative intercooler incorporating a water separator in its high pressure outlet to collect condensate deposited in the high pressure passageways, with a duct seats to transfer this condensate to the inlet of the low pressure passageways, and also incorporating entries to the low pressure passageways for ambient air to be entrained by the flow of low pressure air through injection or ejection devices so as to supplement the cooling action of the low pressure air in that part of the regenerative intercooler operating above ambient tetperature.

2. A regenerative intercooler as claimed in Claim 1 wherein provision is made for ambient air to be entrained by the flow of low pressure regenerative cooling air by using an internal injection configuration, the entrained ambient air mixing with the regenerative cooling air at a location which will enable it to enhance the cooling available to the high pressure air.

3. A regenerative intercooler as claimed in Claim 1 wherein provision is made for anbient air to be entrained by the flow of low pressure regenerative cooling air by using an external ejection configuration, the entrained ambient air entering at a location where the high pressure air is close to ambient tesperature and to flow in passageways essentially parallel with, but separated from, those carrying the low pressure regenerative cooling air.

4. A heat exchanger substantially as described herein with reference to Figures 2-4 in which a flow of air from a cold source is utilised as a coolant, and is eventually to be discharged to the atnosphere, is used to entrain ambient air into the heat exchanger as a secondary cooling medium.